A quick and dirty guide to perfect level changes

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Level changes are often over explained, and too complicated for their own good. There really is nothing to them and if you follow this tutorial step by step, you should have absolutely no trouble whatsoever.

What is a level change?

A level change is, simply put, a transition or displacement from one map (.bsp file) to another. And the reason you're reading this is because you're lost or trying to get a level change to work properly.

Why do I need level changes?

If you're thinking to yourself: "I can get by without them, and save myself a lot of hassle...", then think again!

Half-Life maps have limits. These limits should never be reached or pushed, you can read more about these in the general MAX_MAP limits part of Tommy14's errors page. If your levels are getting too big you should consider splitting them into 2 or more separate levels to avoid reaching these limits. This can be really useful for reducing r_speeds when working with two or more complex areas, or just to help you keep track of where you are in your map. Huge detailed maps are really difficult to work with in Hammer, as you probably already know.

How do I create level changes?

There are 3 types of level changes:

• Seamless: The simplest level change you can have - walk through a corridor, see some loading text, end up in another map, but your position in the corridor and the environment around you does not change. The place you end up in is a carbon copy of the place you have come from.
• Teleport: Same as above only the environment changes - i.e. go through a corridor in a lab and end up in your office/classroom searching for the 'check for problems' button in your life...It is a bit like teleporting, but you are doing it across maps.
• One-way: You can get there, but you can never return.

Seamless level changes

The only entities you'll need - since you just want a simple level change - will be trigger_changelevel (one in each map) and an info_landmark (also one in each map).

Start by making a suitable corridor: Now to add the info_landmark. Read very carefully is these details are critical:

The info_landmark sets up a constant point of reference in the origin and destination maps. It must appear in both maps otherwise the level change will not work correctly. The origin and destination info_landmark must both have the same Name (targetname) So basically, it's the same info_landmark in both maps. To avoid this problem, make sure the level change triggers in the two maps have at least 56 units between them. Players are 32 units wide and long, but their bounding box can become larger if they walk through at an angle. 56 units is enough space to avoid this problem. Now, compile the maps through hammer or any other front-end compiler but remember not to run the game!, fire up hl with the console, and test the transition. If you did this correctly you should seamlessly jump from one map to the next no matter how you enter the trigger_changelevel.

One way level changes

You would think a one way level change would only require one trigger_changelevel?

Wrong.

You have to set the level change up exactly as you would for a normal change. The difference is that in the second map, reduce the size of the trigger_changelevel brush and move it somewhere that the player cannot get to it. That is what stops the player from going back. Also check the Use Only Flag just to make sure those NoClipping players still can't get back.

Teleporting level changes

A teleporting level change is a bit more involved but is actually a lot less of a headache, provided you're only going to make it a one-way affair. It can also be a cheat a modding team can use when passing between chapters where team A work on the previous chapter, and team B work on the next, without worrying about passing the transitional level geometry between the two.

We will assume 2 maps map1 and map2 and the setup is a one-way teleport from map1 to map2.

map1 setup

map2 setup

In map2 the setup can go two ways; the easy way (with favourable conditions) or the other way.

If in the previous map's teleport room the player's position is well constrained close to the info_landmark and the info_teleport_destination is already facing the correct way, then it's simply a matter of placing a single info_landmark at the destination point:

• info_landmark placed at least 36u above the floor
  • Name: tp_landmark

Common problems and solutions

Players stuck in a random place at the other end

Don't forget to add the return trigger_changelevel! Even for testing, the setup pair needs to exist on both maps.
This is exactly what happens when you changelevel through the inaccessible broken elevator in "Forget About Freeman!"

Players transition seamlessly but now stuck at the other end

Make sure both info_landmarks are at the same position relative to the level geometry in the transition area. For example, you cannot have landmark1 16u above the floor in map1 but then have landmark1 64u above the floor in map2. This applies to walls as well.

You may be tempted to offset one of the landmarks to fix a problem, but that's actually creating this exact problem going the other way. Just make sure the landmark is identically positioned.

Some error occurred and now all level changes don't work

You had the two trigger_changelevels too close to each other, making it so that as soon as you changed level, you're inside the other trigger_changelevel. The game engine will freak out about this and disable all level transitions.

The solution is to have the trigger_changelevels further apart from the center of the transitional area. It should be about 56u apart or more face-to-face when you compare the two maps.

I can't make a level change that rotates 90° (or some other angle)

Unfortunately, no you can't (at least not in vanilla Half-Life). The orientation of the transitional areas need to be identical.

Objects (like pushable crates) disappear at the transition area

Brush entities need a unique global name to be able to be "carried over" across levels.